It could be a top app - if...
.. if the developer does something very sensible. Move it to a one-time purchase or, an annual thing to continue receiving updates, but you keep what you have if you don't upgrade. This is what these apps are, by virtue, they are not the type of app people want to pay a monthly/annual subscription for. I honestly believe so many apps out there can be far more sucessful if they get this subscription thing out of their heads. Human beings can only stand so many subscriptions in their lives, & these wee apps are never going to be important enough for it. Keep it simple, keep it sane, one price for an app, sell more volume, get more customers, and ignore the crowd of greedy people subscriptions!